1. Field of the Invention
The present invention relates to a process for recovering products from tar sand, and more particularly, to a combination physical separation process and thermal fluidized bed process for recovering products from the tar sand.
2. The Prior Art
Tar Sands--General Discussion
The term "tar sand" refers to a consolidated mixture of bitumen (commonly referred to as "tar") and sand. Other names used to describe tar sands include "oil sands" and "bituminous sands"--the latter term being more technically correct in that it provides a more accurate description of the mixture. X-ray diffraction patterns reveal that the sand constituent of tar sand is mostly alpha quartz, while the bitumen or tar constituent of tar sand consists of a mixture of a variety of hydrocarbons including heterocyclic compounds. After separation of the bitumen from the sand, the bitumen may be upgraded to a synthetic crude oil suitable for use as a feedstock for the production of such materials as liquid motor fuels, heating oil, and petrochemicals.
About sixty-five percent (65%) of all of the known oil in the world is contained in tar sand deposits or heavy oil deposits. With the exception of the continents of Australia and Antarctica, tar sand fields have been located throughout the world. Significantly, large tar sand deposits have been identified and mapped in Canada, Columbia, Trinidad-Tobago, Venezuela, and the United States. The Canadian tar sand deposits, commonly referred to as the Athabasca tar sands, are located in the province of Alberta, Canada and are currently being developed. It is estimated that the bitumen content in the Athabasca tar sands alone represents approximately 900 billion barrels of bitumen in place.
Analysis of the Athabasca tar sands indicates that these tar sands have an average bitumen content of approximately twelve to thirteen percent (12-13%) by weight. Significantly, the Athabasca tar sands also have a relatively high moisture content of approximately three to five percent (3-5%) by weight connate water. Although not experimentally verified, it is believed by some that the equilibrium structure of the Athabasca tar sands consists of a sand mixed with, but separated from, a bitumen matrix by a film of connate water--the connate water surrounding each grain of sand. It is further believed that the bitumen in the Athabasca tar sands is naturally displaced from the sand grains by the connate water. Whatever the position of the connate water in the Athabasca tar sands, it has been the experience of those skilled in the art that the bitumen phase is readily disengaged from the sand phase by conventional hot water separation techniques.
A more comprehensive discussion of the Athabasca tar sands may be found, for example, in:
(1) E. D. Innes & J. V. D. Tear, "Canada's First Commercial Tar Sand Development," 3 Proceedings of the Seventh World Petroleum Congress 633 (Elsevier Publishing Co., 1967); PA1 (2) F. W. Camp, The Tar Sands of Alberta Canada, Cameron Engineering, Inc., Denver, Colorado (2d ed. 1974); and PA1 (3) J. Leja and C. W. Bowman, "Application of Thermodynamics to the Athabasca Tar Sands," 46 Canadian Journal of Chemical Engineering 479 (1968).
In the United States, approximately twenty-four (24) states are presently known to contain tar sand deposits. However, about ninety to ninety-five percent (90-95%) of the mapped tar sand deposits are located within the state of Utah. These Utah tar sands are estimated to represent at least twenty-five (25) billion barrels of synthetic crude oil. Although the Utah tar sand reserves appear small in comparison with the Athabasca tar sand reserves, Utah tar sands represent a significant energy source when compared to the known natural crude oil reserves in the United States (approximately 31 billion barrels).
For the most part, the Utah tar sand reserves are deposited in six major locations along the eastern edge of Utah, with the bitumen content varying from deposit to deposit as well as within a given deposit. Generally, Utah tar sand deposits contain less than ten percent (10%) bitumen by weight, although deposits have been found with higher bitumen content.
Unlike Athabasca tar sands, however, Utah tar sands contain a negligible amount of connate water (much less than one percent (1%) by weight), and are most commonly characterized by a virtual absence of connate water. Indeed, some Utah tar sands have been found to be so dry that no moisture content can be detected by a standard Dean-Stark analysis. In the absence of connate water, the bitumen in the Utah tar sands is directly in contact with and bonded to the surface of the sand grains.
Moreover, tests have determined that the bitumen in Utah tar sands is at least ten times, and often as much as a thousand times, more viscous than the bitumen in Athabasca tar sands. (See FIG. 1 for an Arrhenius-type plot illustrating the effect of temperature on the bitumen viscosity in both Utah and Athabasca tar sands). Indeed, certain Utah tar sand samples taken from an area known as the Tar Sand Triangle have been found to be well over ten thousand times more viscous than the Athabasca tar sands.
In view of the recognized physical and chemical differences between Utah tar sands and Athabasca tar sands, it will be readily appreciated that the processing of Utah tar sands is substantially more difficult than the processing of Athabasca tar sands. The processing of Utah tar sands involves two fundamental steps: (1) displacing the bonded bitumen from the sand grains, and (2) disengaging the viscous bitumen phase from the residual sand phase. It may be that the processing of Athabasca tar sands merely involves disengaging the relatively less viscous bitumen phase from the sand phase, since the bitumen may already be displaced from the sand by a film of connate water. However the connate water and the relatively less viscous bitumen in the Athabasca tar sands might function to facilitate the separation of the bitumen from the sand, it is clear that the processing of the Athabasca tar sands substantially easier than the processing of Utah tar sands.
It is, therefore, not surprising that the separation processes which have been successfully applied to the Athabasca tar sands have been unsuccessful in processing Utah tar sands. A few methods have been specifically developed for processing Utah tar sands and are disclosed in (1) U.S. Pat. No. 4,120,776 entitled "SEPARATION OF BITUMEN FROM DRY TAR SANDS," which patent issued on Oct. 17, 1978 to Jan D. Miller et al.; and (2) U.S. patent application Ser. No. 194,515, filed Oct. 6, 1980 by Jan D. Miller et al. for "PROCESS FOR SEPARATING HIGH VISCOSITY BITUMEN FROM TAR SANDS"; which patent and patent application are both incorporated herein by reference.
U.S. Pat. No. 4,120,776 discloses an alkaline, hot water separation process for recovering bitumen from Utah tar sands. Patent application Ser. No. 194,515, filed Oct. 6, 1980, discloses an ambient temperature grinding and flotation process for separating bitumen from sand in tar sands containing highly viscous bitumen, such as the Utah tar sands.